This application claims the priority of German Patent Application, Serial No. 299 14 126.8, filed Aug. 12, 1999, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a linear drive, and more particularly to a linear drive of a type having a spindle, and a drive mechanism, including a drive motor and a reduction gear in driving relationship with the drive motor, for rotatably driving the spindle.
Linear drives of this type are typically employed for adjusting a position of components of pieces of furniture. Thus, the power output of such linear drives is relatively low. The drive motor is normally a d.c. motor with applied safety voltage. The reduction gear significantly decreases the revolution of the spindle with respect to the motor shaft. Moreover, the linear drive has a casing. When the spindle rotates, a spindle nut, placed on the spindle in fixed rotative engagement, travels linearly to operate the attached component of the piece of furniture via a lever or similar part.
Typically, linear drives, involved here, are single drives with one drive motor, a reduction gear and a spindle, or dual drives with two drive motors and two reduction gears as well as two spindles, with each drive motor being individually activated. Thus, each drive mechanism is comprised of the drive motor, the reduction gear and the spindle, whereby the reduction gear is normally a worm gear, with the worm placed directly on the output pin of the drive motor. Thus, the motor shaft extends at a right angle to the spindle. As a consequence, the linear drive can be installed in specific space configuration only, and is thus not universally applicable.
Linear drives are also known having a motor shaft in driving relation with the spindle via bevel wheels. Such drives are, however, unsuitable for use as drives for pieces of furniture because the speed ratio of the motor shaft in relation to the spindle is fairly small, so that the spindle nut would run way too fast.
It is thus an object of the present invention to provide an improved linear drive, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved linear drive which is simple in structure and compact while yet running quietly and reliably in operation.
It is another object of the present invention to provide an improved linear drive which allows a disposition of a drive motor in any desired manner with respect to the spindle.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing at least one spindle, and a drive mechanism, including a drive motor and a reduction gear in driving relationship with the drive motor, for rotatably driving the spindle, with the drive mechanism having a drive element having an input member and an output member, whereby the input member is selectively adjustable with respect to the output member.
In accordance with the present invention, the drive mechanism is expanded by the adjustable drive element. The position of the input element with respect to the output member depends on the installation conditions at hand. Although a perpendicular disposition of the motor shaft with respect to the spindle is basically possible, the distance of the drive motor to the spindle can be greatly modified, so that other configurations of the drive motor with respect to the spindle are now feasible as well, e.g. a non-perpendicular disposition. It is also possible to disengage the drive motor from the remaining components so that the drive motor can be mounted at a free location. This is advantageous in particular in narrow or tight spaces of installation, as the adjustable drive element permits installation of the drive motor at any suitable location. The drive element with an adjustment option of the output member with respect to the input element, or vice versa, is normally so configured that the transmitted torque is relative small and sufficient to adjust components of a piece of furniture, e.g. slatted frames, components of a chair or the like. As the linear drive is so mounted to a piece of furniture that its components are invisible, the provision of the additional drive element does not increase a risk of accident. A need for a particular protection is thus not necessary and the linear drive operates extremely quiet.
According to another feature of the present invention, the input member of the drive element is infinitely variable with respect to the output member within an adjustment range. In this way, the drive motor can be positioned in any disposition to the spindle. Suitable, the drive element is a strand-like, flexible element, or includes at least a joint, e.g. a ball-and-socket joint or a universal joint. A strand-like drive element may, for example, be implemented by a flexible shaft, whereas for the application of a joint, the use of a cardan shaft or an articulated shaft are conceivable. In the event the drive element has several spaced-apart joints, the entire deflection angle may be relatively great. It is, however, also feasible to provide the drive mechanism with at least two different drive elements, e.g. one or more strand-like, flexible drive elements and one or more ball-and-socket joints or cardan joints, so that any suitable combination can be used and best suited to the installation conditions at hand.
Suitably, the drive motor and the reduction gear are coupled in driving relationship by the adjustable drive element. This configuration is advantageous because a smallest torque can be transmitted whereas at a linkage, for example between the reduction gear and the spindle, that is basically possible, the drive element can transmit a respectively high torque.
The drive motor can be randomly located. It is therefore possible, that the drive motor has a rotor destined from rotation about a rotation axis which extends in parallel relation at a distance to a rotation axis of the spindle. The spindle is fitted in a so-called flanged tube which is securely fixed to the casing, so that the drive motor may be mounted on the outside directly upon the flanged tube. Depending on the option of installing the linear drive in free spaces of a piece of furniture, the rotation axis of the rotor of the drive motor may also extend at slanted disposition to the rotation axis of the spindle. Suitable, the spindle and the motor shaft define hereby an acute angle. It is also possible, to secure the drive motor by a bracket which is mounted to the casing or to the flanged tube.
According to another feature of the present invention, the reduction gear may be a worm gear having a worm coupled to the drive element. In this manner, a relatively great speed ratio of the drive motor to the spindle can be realized.
When employing the linear drive as drive for a piece of furniture, the attached component of the piece of furniture is operated by the linear drive for moving the component and thus the piece of furniture in up and down directions. Situations are, however, conceivable, when the down movement is implemented at a greater speed as a result of the own weight. In this case, the linear drive should be configured with a release clutch for coupling the drive element with the drive motor so that the linear drive can be disengaged.
According to another feature of the present invention, the drive element may be formed by a plurality of windings wound from a wire. In this manner, the drive element can be shaped or deformed to suit any situation at hand and is easy to manufacture. An alternative that permits an increase of the torque being transmitted includes the fabrication of a strand-like, flexible drive element from several layers which are nested within one another and made from windings of different diameter. As a consequence, the wall thickness of the drive element is increased.
The use of a drive element with an input member that is adjustable with respect to the output member permits further options. For example, several linear drives of conventional design may be united to a drive assembly, with the gear mechanism of each linear drive driven by the drive element via a transfer case. It is then possible, to use a single motor to drive several linear drives, whereby a transfer case is disposed between the motor and the linear drives. Another variation includes the use of two or more transfer cases that are driven by a single motor, wherein the drive elements of the linear motors are connected to the output elements of the transfer cases.
Suitably, the drive motor is activated by a hand switch via a control unit which is operatively connected to the hand switch. It may also be conceivable to so configure the transfer cases that only selected linear drives are operated when the drive motor is switched on.